The prior art contains a multiplicity of air-operated paint spraying devices which generally comprise a paint reservoir, a device for generating an air flow, for example, a compressor or a blower and a spray gun.
In the case of what are termed HVLP systems (high volume, low pressure), the paint is atomized by means of an air blower through a high volume flow rate of air at a low pressure at a spray head. To that end, the paint is provided at the spray head either by means of a conveying air pressure or otherwise. The quantity of paint dispensed is generally regulated by a needle valve and a trigger mechanism. The air blower and the paint supply are integrated either into the pistol unit or alternatively individually or together in a base station. Such an HVLP atomization is for example mentioned in US 2011/0073677 A1. A transportable spray device with an operating unit, a paint spraying lance and a spray head and separate paint reservoir is described in WO 2011/038712 A1.
In order to convey the paint from a paint reservoir which is remote from a paint spraying gun to the paint spraying gun, in particular, in the case of high-viscosity paints, substantial pressures are required. The required conveying pressure is then dictated, in particular, by the length of the line used and the cross section thereof. The spraying process at the spray head itself should, however, take place with an appropriately low pressure in order to avoid an uncontrolled egress of paint, known as “spitting”, upon opening a needle valve on the spray head. If this is not done, the application of paint is uneven on account of variations in the quantity of atomizable paint dispensed at the paint spraying head. In the prior art, this effect is avoided by switching the paint conveying on and off according to the quantity of paint to be dispensed. However, this requires complex and rapid switching processes which make the relevant devices complicated, susceptible to faults and expensive.